You do know that this info is readilty available in the help files right?
As Loopylou correctly pointed out, you must have the cluster featureID code programmed correctly in your cluster form.
For Call Forward Follow Me (Third-Party) and I Am Here forwarding, enable Call Forwarding Accept in the Class of Service Options form of the forward destination.
To program Call Forward:
Press SuperKey.
Press No until "Call Forwarding?" appears.
Press Yes.
Press Next until the type of Call Forward appears.
Press Review.
If a number is already programmed, press Change.
Press Program.
Do one of the following:
Dial the destination number.
For Call Forward I Am Here, dial your extension number.
Press Save.
Press SuperKey.
To turn Call Forward on or off (once it has been set up):
Press SuperKey.
Press No until Call Forwarding appears.
Press Yes.
Press Next until the type of Call Forward appears.
Press Review.
Press Change.
Do one of the following:
To turn Call Forward on, press TurnOn.
To turn Call Forward off, press TurnOff.
Press SuperKey.
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Occam's Razor - All things being equal, the simplest solution is the right one.